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.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
.TH "HCREATE" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" hcreate
.SH NAME
hcreate, hdestroy, hsearch \- manage hash search table
.SH SYNOPSIS
.LP
\fB#include <search.h>
.br
.sp
int hcreate(size_t\fP \fInel\fP\fB);
.br
void hdestroy(void);
.br
ENTRY *hsearch(ENTRY\fP \fIitem\fP\fB, ACTION\fP \fIaction\fP\fB);
\fP
\fB
.br
\fP
.SH DESCRIPTION
.LP
The \fIhcreate\fP(), \fIhdestroy\fP(), and \fIhsearch\fP() functions
shall manage hash search tables.
.LP
The \fIhcreate\fP() function shall allocate sufficient space for the
table, and the application shall ensure it is called
before \fIhsearch\fP() is used. The \fInel\fP argument is an estimate
of the maximum number of entries that the table shall
contain. This number may be adjusted upward by the algorithm in order
to obtain certain mathematically favorable circumstances.
.LP
The \fIhdestroy\fP() function shall dispose of the search table, and
may be followed by another call to \fIhcreate\fP(). After
the call to \fIhdestroy\fP(), the data can no longer be considered
accessible.
.LP
The \fIhsearch\fP() function is a hash-table search routine. It shall
return a pointer into a hash table indicating the
location at which an entry can be found. The \fIitem\fP argument is
a structure of type \fBENTRY\fP (defined in the \fI<search.h>\fP header)
containing two pointers: \fIitem.key\fP points to the comparison
key (a \fBchar *\fP), and \fIitem.data\fP (a \fBvoid *\fP) points
to any other data to be associated with that key. The
comparison function used by \fIhsearch\fP() is \fIstrcmp\fP(). The
\fIaction\fP argument
is a member of an enumeration type \fBACTION\fP indicating the disposition
of the entry if it cannot be found in the table. ENTER
indicates that the item should be inserted in the table at an appropriate
point. FIND indicates that no entry should be made.
Unsuccessful resolution is indicated by the return of a null pointer.
.LP
These functions need not be reentrant. A function that is not required
to be reentrant is not required to be thread-safe.
.SH RETURN VALUE
.LP
The \fIhcreate\fP() function shall return 0 if it cannot allocate
sufficient space for the table; otherwise, it shall return
non-zero.
.LP
The \fIhdestroy\fP() function shall not return a value.
.LP
The \fIhsearch\fP() function shall return a null pointer if either
the action is FIND and the item could not be found or the
action is ENTER and the table is full.
.SH ERRORS
.LP
The \fIhcreate\fP() and \fIhsearch\fP() functions may fail if:
.TP 7
.B ENOMEM
Insufficient storage space is available.
.sp
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.LP
The following example reads in strings followed by two numbers and
stores them in a hash table, discarding duplicates. It then
reads in strings and finds the matching entry in the hash table and
prints it out.
.sp
.RS
.nf
\fB#include <stdio.h>
#include <search.h>
#include <string.h>
.sp
struct info { /* This is the info stored in the table */
int age, room; /* other than the key. */
};
.sp
#define NUM_EMPL 5000 /* # of elements in search table. */
.sp
int main(void)
{
char string_space[NUM_EMPL*20]; /* Space to store strings. */
struct info info_space[NUM_EMPL]; /* Space to store employee info. */
char *str_ptr = string_space; /* Next space in string_space. */
struct info *info_ptr = info_space;
/* Next space in info_space. */
ENTRY item;
ENTRY *found_item; /* Name to look for in table. */
char name_to_find[30];
.sp
int i = 0;
.sp
/* Create table; no error checking is performed. */
(void) hcreate(NUM_EMPL);
while (scanf("%s%d%d", str_ptr, &info_ptr->age,
&info_ptr->room) != EOF && i++ < NUM_EMPL) {
.sp
/* Put information in structure, and structure in item. */
item.key = str_ptr;
item.data = info_ptr;
str_ptr += strlen(str_ptr) + 1;
info_ptr++;
.sp
/* Put item into table. */
(void) hsearch(item, ENTER);
}
.sp
/* Access table. */
item.key = name_to_find;
while (scanf("%s", item.key) != EOF) {
if ((found_item = hsearch(item, FIND)) != NULL) {
.sp
/* If item is in the table. */
(void)printf("found %s, age = %d, room = %d\\n",
found_item->key,
((struct info *)found_item->data)->age,
((struct info *)found_item->data)->room);
} else
(void)printf("no such employee %s\\n", name_to_find);
}
return 0;
}
\fP
.fi
.RE
.SH APPLICATION USAGE
.LP
The \fIhcreate\fP() and \fIhsearch\fP() functions may use \fImalloc\fP()
to allocate
space.
.SH RATIONALE
.LP
None.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIbsearch\fP() , \fIlsearch\fP() , \fImalloc\fP() , \fIstrcmp\fP()
, \fItsearch\fP() , the
Base Definitions volume of IEEE\ Std\ 1003.1-2001, \fI<search.h>\fP
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
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